For some time it has been well-known that cacao beans contain a small amount of caffeine (1,3,7 trimethylxanthine) and a considerably larger amount of theobromine (3,7 dimethylxanthine). The relationship, depending upon the particular variety of cacao bean, ranges from about a ratio of two to one theobromine to caffeine to about ten to one theobromine to caffeine. Moreover, it has been found that theobromine is about 100 times less soluble in water than caffeine. The effective removal of these methylxanthines from cacao beans, therefore, must deal primarily with processes which will remove a large percentage of the relatively insoluble theobromine while at the same time removing the relatively smaller amounts of the more soluble caffeine. The present invention is directed to an improved process for the treatment of cacao beans or cacao nibs to remove methylxanthines consisting of theobromine and caffeine. Such xanthines are members of a broader chemical class known as purines. The purine system is composed of a pyrimidine ring and an imidazole ring fused together. The rings of the purine molecule are numbered starting with the nitrogen atom at the upper left corner of the pyrimidine ring and proceeding counterclockwise to the number 6 position and then proceeding clockwise from the pyrimidine number 5 position to give the 7, 8 and 9 positions in the imidazole ring. The dihydroxy purines are known as xanthines and are numbered in the same way. This nomenclature system is used throughout the present specification.
Various methods for accomplishing the removal of such methylxanthines from cacao material have been proposed heretofore. One such prior process involves the extraction of these methylxanthines by use of chlorinated hydrocarbon solvents, such as chloroform, ethylene dichloride or tetrachlorethane. Such solvent extraction processes are shown in U.S. Pat. Nos. 1,073,441, 1,855,026 and 1,925,326, respectively. However, the use of such extraction solvents is not recommended, particularly where food products are involved, since residues of such solvents are undesirable in a food product. Another method of removing theobromine from cacao beans involves extraction with water and then treating the aqueous extract with an adsorbent in subdivided form. While this method does not involve the use of objectionable chemicals, such as chlorinated hydrocarbon solvents, there are certain difficulties connected with the use of such adsorbent materials which adversely affect the taste of the final depurinized cacao product. Moreover, the percentage removal of theobromine is limited.
Still another prior process for extracting methylxanthines from cacao material comprises contacting the cacao material, swollen by treatment with a relatively small amount of water, with a food-acceptable solvent gas such as supercritical nitruns oxide or supercritical carbon dioxide. However, this process requires long treatment times and frequently does not achieve a sufficient percentage reduction in the theobromine content. Moreover, the removal of the methylxanthines from the supercritical gas presents a problem where, as is usually the case, it is desired to re-use the supercritical gas.
Still another process for removing caffeine from coffee is disclosed in U.S. Pat. No. 4,474,821 in which a countercurrent extraction process using a plurality of extraction vessels in the countercurrent operation is disclosed. However, in the process of this patent an extraction solvent consisting of ethyl acetate plus water is employed in which the ethyl acetate-water azeotrope is ultimately removed by differential pressure steam stripping. In the process of this patent turbulent flow of the extracting solvent is used to obtain an accelerated decaffeination rate which, in turn, reduces the caffeine extraction time. This prior process, as well as other extraction processes which utilize organic solvents, has the disadvantage of requiring that most of the product mass or water extract be exposed to the solvent.